The present invention relates to the structure of flanged tape reels housed in a cassette case comprising an upper cassette half and a lower cassette half.
A magnetic tape cassette widely used with audio or video equipment comprises upper and lower cassette halves molded from synthetic resin, or the like, and a pair of spools which have a magnetic tape wound thereon (e.g., reels or hubs) and are stored in the upper and lower cassette halves.
FIG. 1 is a perspective exploded view showing the principal constituent parts of a VTR magnetic tape cassette. A pair of flanged tape reels 2 on which a magnetic tape 1 is wound is housed in a cassette case comprising an upper cassette half 3 and a lower cassette half 4. A tape draw opening formed in the front portion of the cassette case is covered with a guard panel 5.
The upper cassette half 3 has a box-shaped profile and comprises a rectangular upper wall surface 6 having an opening for use as a window formed therein; a front side wall 7, a rear side wall 8, and lateral side walls 9, 9, all of which extend at right angles from the peripheral edge of the upper wall surface 6. The upper cassette half 3 is integrally formed from ABS resin, or the like, and a transparent window is welded to the upper wall surface 6. A leaf spring (not shown) for forcing the flanged tape reels 2 in a downward direction of the cassette is mounted at the center of the reverse side of the upper wall surface 6.
Similarly, the lower cassette half 4 has a box-shaped profile and comprises a rectangular lower wall surface 10, and longitudinal side walls 11, 12 and lateral side walls 13, 13, all of which extend at right angles from the peripheral edge of the bottom wall surface 10. Openings 15 are formed in the bottom wall surface 10 so as to permit insertion of drive shafts of a record/play device into reel hubs 14 of the flanged tape reels 2.
Partition walls 16 formed in a substantially circular pattern and extending upright from the upper wall surface 9 within the upper cassette half 3 and partition walls 16 formed in a substantially circular pattern and extending upright from the bottom wall surface 10 within the lower cassette half 4 abut each other so as to surround the flanged tape reels 2 within the cassette. The horizontal positions of the flanged tape reels 2 are restricted by coming into contact with the partition walls 16.
Each of the flanged tape reels 2 comprises a transparent disk-shaped flange 17 having an upper flange through hole 18 formed therein and a disk-shaped lower flange 19 integrally formed with a columnar reel hub 14. The lower flanges 19 are formed from highly-abrasion-resistant resin such as polyoxyethylene (POM), or the like.
FIG. 2 shows a conventional flanged tape reel 2 in detail. For the purpose of holding the end of a magnetic tape 1, a cutout 21 is formed in part of the circumferential surface of the reel hub 14 in the form of a combination of an opening and an internally-recessed cavity which is wider than the opening, thereby enabling a clamp pin 20 which serves as a clamp member to be fitted into the cavity from the outside in the radial direction of the reel hub 14.
The clamp pin 20 is a base member having the same curvature as that of the reel hub 14 and has a substantially C-shaped cross section in the direction perpendicular to the rotation axis of the magnetic tape 1. A side edge 22 externally protrudes from each open end of the clamp pin 20 in the circumferential direction of the reel hub 14 and has a taper 23.
FIG. 3 shows a conventional method of fitting the clamp pin 20 into the cutout 21. After the upper and lower flanges 17 and 19 have been joined together, the clamp pin 20 is inserted into the lower flange 19 through the upper flange through hole 18 and is fitted into the cutout 21 from the outside in the radial direction of the reel hub 14 so as to hold the magnetic tape 1. In order to prevent the clamp pin 20 from interfering with the upper and lower flanges 17 and 19 when being fitted into the cutout 21, as well as to firmly hold the end of the magnetic tape 1, the clamp pin 20 has substantially the same height as an interval between the lower surface of the upper flange 17 and the upper surface of the lower flange 19 in the axial direction of the reel 14. Namely, the clamp pin 20 has substantially the same height as that of the area of the reel hub 14 on which the magnetic tape 1 is wound.
In the aforementioned conventional reel for use with a magnetic tape cassette, the end of the magnetic tape is held as a result of the side edges 22 of the clamp pin 20 engaging guide protuberances 24 of the cutout 21. Accordingly, if the fitting force of the clamp pin 20 is reduced in order to improve the ease of assembly, a risk may arise of releasing the magnetic tape 1. In contrast, if an attempt is made to improve the force of the clamp pin 20 for holding the magnetic tape 1 by reducing the interval between the clamp pin 20 and the cutout 21, a risk may arise of cutting the magnetic tape. This is a first problem in the conventional technique.
In addition, a conventional reel for use in a magnetic tape cassette generally comprises a substantially-cylindrical reel body, an upper circular flange attached to one end of the reel body, and a lower circular flange attached to the other end of the reel body. With regard to this reel, there are demands for the upper and lower flanges being coaxially aligned in parallel with each other, as well as for the outer peripheries of the upper and lower flanges being aligned to each other. As shown in FIG. 4, bosses 155 are formed on an upper surface 154 of a top wall 153 of a reel body 152 (called as reel hub) integrally formed with a lower flange 151. The plurality of bosses 155 are provided around a pivot 156 at substantially equal intervals in a circumferential direction. Holes 158 are formed in the corresponding positions on an upper flange 157 so as to receive the bosses 155.
The upper flange 157 is brought into contact with the top wall 153 of the reel body 152 in such a way that the bosses 158 engage with the hole 158. The upper flange 157 is bonded to the reel body 152 by ultrasonically welding the bosses 155.
The reel body 152 comprises an inner peripheral wall 159 into which a hub is fitted, and an outer peripheral wall 160 on which a magnetic tape is wound. The inner peripheral wall 159 and the outer peripheral wall 160 are joined together by a plurality of ribs 161 radially provided around the pivot 156 at substantially equal angles in the circumferential direction. Specifically, since the upper surface 154 of the top wall 153 is formed in parallel with the lower flange 151, the upper and lower flanges 157 and 151 are positioned in parallel with each other by bringing the bosses 155 into engagement with the holes 158. In addition, the outer peripheries of the upper and lower flanges 157 and 151 are coaxially aligned to each other.
In the aforementioned conventional reel for use in a magnetic tape cassette, the top wall 153 of the reel body 152 is positioned at the center and has a small area. Further, there is so-called play between the bosses 155 and the holes 158, because the diameter of the boss 155 is smaller than that of the hole 158. For these reasons, there possibly arises a case where the upper and lower flanges 157 and 151 are held in an insufficiently parallel and coaxial relationship with each other. This is a second problem in the conventional technique.